1. Field of the Invention
This invention relates to a semiconductor device having a low dielectric constant film and a manufacturing method thereof.
2. Description of the Related Art
A so-called chip size package (CSP) is known from Jpn. Pat. Appln. KOKAI Publication No. 2008-244383. This semiconductor device comprises a semiconductor substrate. A first insulating film is provided on the upper surface of the semiconductor substrate. A plurality of wiring lines are provided on the upper surface of the first insulating film. A columnar electrode is provided on the upper surface of a connection pad portion of the wiring line. A second insulating film is provided on the surface of the wiring line, the outer peripheral surface of the columnar electrode and the upper surface of the first insulating film. A sealing film is provided on the upper surface of the second insulating film around the second insulating film provided on the outer peripheral surface of the columnar electrode. A solder ball is provided on the upper surface of the columnar electrode.
In this case, the second insulating film is made of, for example, a polyimide resin. The polyimide resin is a material lower in water absorption coefficient than an epoxy resin which is a material of the sealing film. The use of such a material is intended to prevent a short circuit from being easily caused by electromigration across the wiring lines. Specifically, when no second insulating film is formed, the wiring lines are directly covered with the sealing film made of the epoxy resin. Therefore, a metal (copper) in the wiring lines may ionize and melt due to the electromigration. The melted ions may diffuse into the sealing film, and a short circuit may occur between the wiring lines.
Thus, the wiring lines are covered with the second insulating film made of the polyimide resin lower in water absorption coefficient than the epoxy resin which is the material of the sealing film. As a result, the electromigration does not occur easily. This makes it possible to prevent a short circuit from being easily caused by the electromigration across the wiring lines.
In the meantime, according to the above-mentioned conventional semiconductor device manufacturing method, the second insulating film made of the polyimide resin is formed by, for example, a spin coat method all over the surface of the wiring line, the outer peripheral surface of the columnar electrode and the upper surface of the first insulating film on the semiconductor substrate in a wafer state (hereinafter referred to as a semiconductor wafer). Therefore, the semiconductor wafer contracts due to the curing of the second insulating film, and relatively greatly warps accordingly. The warping of the semiconductor wafer may be disadvantageous to the subsequent steps.